Add from_single_file() support for Ideogram4 and Krea2 transformers

[buffett0323]

What does this PR do?

Adds from_single_file() support for Ideogram4Transformer2DModel and
Krea2Transformer2DModel.

Fixes #14122

Before submitting

• Did you use an AI agent (Claude Code, Codex, Cursor, etc.) to help with this PR? If so:
  • Did you read the Coding with AI agents guide?
  • Did you self-review the diff against .ai/review-rules.md?
• Did you read the contributor guideline?
• Did you read our philosophy doc? (important for complex PRs)
• Was this discussed/approved via a GitHub issue or the forum? Please add a link to it if that's the case.
  • Issue: from_single_file() support missing/incomplete for Ideogram4 and Krea2 transformers #14122
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?
• Are you the author (or part of the team) of the model/pipeline (only applicable for model/pipeline related PRs)?

Who can review?

@sayakpaul @yiyixuxu @DN6

[DN6]

Could we add a check to infer the model type automatically

diffusers/src/diffusers/loaders/single_file_utils.py

Line 586 in d1b988b

def infer_diffusers_model_type(checkpoint):